High solids acid etch and mar resistant clear coating composition

ABSTRACT

The present invention provides for an etch and mar resistant low VOC clear coating composition most suitable for use as a top clear coat in multi-layered OEM or refinish automotive coatings. The coating composition includes polyisocyanate, polyester polyol and melamine components, where more than half of total composition solids include the polyester polyol and melamine components. The polyisocyanate component includes an aliphatic polyisocyanate. The composition may be formulated as a two-pack or one-pack coating composition, wherein the isocyanate functionalities are blocked with a blocker such as a mono-alcohol.

CROSS-REFERENCE TO PARENT APPLICATIONS

This application is a 35 U.S.C. §371 of PCT/US00/06961 filed on Mar. 16,2000, which claims benefit of provisional Application Ser. Nos.60/124,850, filed Mar. 17, 1999 and Ser. No. 60/183,185, filed Feb. 17,2000.

BACKGROUND OF THE INVENTION

The present invention generally relates to high solids, low VOC(volatile organic component) coating compositions and more particularlyto low VOC clear coating compositions suited for multi-layered coatingsused in automotive OEM and refinish applications.

Basecoat-clearcoat systems have found wide acceptance in the automotivefinishes market. Continuing effort has been directed to improve theoverall appearance, the clarity of the topcoat, and the resistance todeterioration of these coating systems at ever-higher application solidslevels. Further effort has also been directed to the development ofcoating compositions having low VOC. A continuing need still exists forclear coating formulations having an outstanding balance of performancecharacteristics after application, particularly etch and mar resistanceat high solids levels and low coating application viscosity.Melamine/acrylic polyol crosslinked or melamine self-condensed coatingsfor example, may provide coatings having acceptable mar but suchcoatings have poor acid etch resistance and decreased appearance athigher solids level. On the other hand, isocyanate/acrylic polyol based2 K urethane coatings generally provide acceptable acid-etch resistancebut such coatings have poor mar resistance. Therefore, a need stillexists for coatings that not only provide acceptable mar and acid-etchresistance but also high gloss and DOI at the lowest VOC possible.

One approach described by Ntsihlele and Pizzi in an article titled“Cross-Linked Coatings by Co-Reaction of Isocyanate-MethoxymethylMelamine Systems” (Journal of Applied Polymer Science, Volume 55, Pages153-161-1995) provides for reacting aromatic diisocyanate withmethoxymethyl melamine. However, a need still exists for a high solidsclear coating composition, which upon a long-term exposure to sunlightdoes not yellow or become brittle and provides low coating applicationviscosities.

Another approach is disclosed in FR-A-2 265 828 provides for heathardenable compositions suitable for coating metal objects. Thecomposition includes a finely divided solid isocyanated polyester resinhaving masked isocyanate groups dispersed in a reactive liquid of highlyetherized metylolated aminotriazine.

STATEMENT OF THE INVENTION

The present invention is directed to a clear coating compositioncomprising a polyester polyol a polyisocyanate and a melamine componentwherein the total amount of said polyisocyanate and melamine componentsrange from 50 percent to 90 percent, said percentages being in weightpercentage based on the total weight of composition solids and whereinsaid polyisocyanate component comprises an aliphatic polyisocyanatehaving on an average 2 to 6 isocyanate functionalities.

The present invention is also directed to a method of producing a clearcoating on a substrate comprising:

applying a layer of a clear coating composition comprising a polyesterpolyol, a polyisocyanate and a melamine component wherein the totalamount of said polyisocyanate and melamine components range from 50percent to 90 percent, said percentages being in weight percentage basedon the total weight of composition solids and wherein saidpolyisocyanate component comprises an aliphatic polyisocyanate having onan average 2 to 6 isocyanate functionalities; and

curing said layer into said clear coating.

One of the advantages of the present invention is its low VOC, which isbelow the current guidelines of Environment Protection Agency (EPA) ofthe United States.

Another advantage is the mar and etch resistance and hardness of thecoating resulting from the coating composition of the present invention.

Yet another advantage is the clarity and high gloss of the coatingresulting from the coating composition of the present invention.

As Used Herein:

“Two-pack coating composition” means a thermoset coating compositioncomprising two components stored in separate containers. Thesecontainers are typically sealed to increase the shelf life of thecomponents of the coating composition. The components are mixed prior touse to form a pot mix. The pot mix has a limited pot life typically ofminutes (15 minutes to 45 minutes) to a few hours (4 hours to 6 hours).The pot mix is applied as a layer of desired thickness on a substratesurface, such as an autobody. After application, the layer is curedunder ambient conditions or bake cured at elevated temperatures to forma coating on the substrate surface having desired coating properties,such as high gloss, mar-resistance and resistance to environmentaletching. “One-pack coating composition” means a thermoset coatingcomposition comprising two components that are stored in the samecontainer. However, one component is blocked to prevent prematurecrosslinking. After the application of the one-pack coating compositionon a substrate, the layer is typically exposed to elevated temperaturesto unmask the blocked component. Thereafter, the layer is bake-cured atelevated temperatures to form a coating on the substrate surface havingdesired coating properties, such as high gloss, mar-resistance andresistance to environmental etching.

“Low VOC coating composition” means a coating composition that includesin the range of from 0 to 0.472 kilogram of organic solvent per liter (4pounds per gallon), preferable in the range of from 0.118 (1 pound pergallon) to 0.295 kilogram of organic solvent per liter (2.5 pounds pergallon) of the composition, as determined under the procedure providedin ASTM D3960.

“High solids composition” means a coating composition having a solidcomponent in the range of from 65 to 100 percent and preferably greaterthan 70 percent, all in weight percentages based on the total weight ofthe composition.

“Clear coating composition” means a clear coating composition thatproduces upon cure, a clear coating having DOI (distinctness of image)rating of more than 80 and 20° gloss rating of more than 80.

“GPC weight average molecular weight” and “GPC number average molecularweight” means a weight average molecular weight and a weight averagemolecular weight, respectively measured by utilizing gel permeationchromatography. A high performance liquid chromatograph (HPLC) suppliedby Hewlett-Packard; Palo Alto, Calif. was used. Unless stated otherwise,the liquid phase used was tetrahydrofuran and the standard waspolystyrene.

“Polymer particle size” means the diameter of the polymer particlesmeasured by using a Brookhaven Model BI-90 Particle Sizer supplied byBrookhaven Instruments Corporation, Holtsville, N.Y. The sizer employs aquasi-elastic light scattering technique to measure the size of thepolymer particles. The intensity of the scattering is a function ofparticle size. The diameter based on an intensity weighted average isused. This technique is described in Chapter 3, pages 48-61, entitledUses and Abuses of Photon Correlation Spectroscopy in Particle Sizing byWeiner et al. 1987 edition of American Chemical Society Symposiumseries.

“Polymer solids” or “composition solids” means a polymer or compositionin its dry state.

“Aliphatic” as employed herein includes aliphatic and cycloaliphaticmaterials.

“Crosslinkable” means that the individual components of a compositioncontain functionalities, which react within the composition of theinvention to give a coating of good appearance, durability, hardness andmar resistance.

“Acid etch resistance” refers to the resistance provided by a coatedsurface against chemical etching action by the environment, such as forexample acid rain.

“Mar resistance” refers to the resistance provided by coating tomechanical abrasions, such as, for example, the abrasion of a coatedsurface, such as an automotive body, that typically occurs duringwashing and cleaning of the coated surface.

Applicants have unexpectedly discovered that contrary to conventionalapproaches used in typical thermoset coating compositions, i.e., thoseinvolving polymers and crosslinking components, a very viable route liesin a combination of what would traditionally be considered ascrosslinking agents for producing a unique low VOC high solids clearcoating composition that produces coatings having superior coatingproperties, such as clarity, and mar and etch resistance.

When a coating composition of polyisocyanate and melamine formulatedwith more than 50 weight percent based on total composition solids ofmelamine is employed, etch resistance drops rapidly. The durabilitybased on accelerated weathering also suffers. It is believed, withoutreliance thereon, that the higher weight percentage of melamine in thecoating composition leads to self-condensed melamine, which in turnadversely affects the coating durability.

On the other hand, if one were to formulate a clear coating compositionwith more than 55 weight percent based on total composition solids ofpolyisocyanate, such as isocyanurate of hexamethyl diisocyanate, marresistance of the resultant coatings suffers. Other aliphaticisocyanates, such as the trimers of isophorone diisocyanate, used atthese levels would also be unsatisfactory as such high levels would leadto higher coating application viscosities, which in turn would requirehigher solvent loading. As a result, the VOC of the composition will beunacceptably high. Thus a need exists to provide a low VOC coatingcomposition that not only has good mar and itch resistance but it alsohas low coating application viscosity.

Applicants have unexpectedly discovered that by substantially increasingthe total amount of polyisocyanate and melamine components in a coatingcomposition, provided neither component is more than about half of thetotal composition solids, results in a low VOC clear coating compositionhaving improved mar and etch resistance coupled with low applicationviscosity so long as a polyester polyol is also included. Low molecularweight polyester polyols are preferred as even lower coating applicationviscosities can be obtained. Moreover, the foregoing combination alsodoes not adversely affect other important coating properties, such asgloss, DOI, and other desired coating properties.

The clear coating composition of the present invention includes apolyester polyol, a polyisocyanate and a melamine components wherein thetotal amount of the polyisocyanate and melamine components ranges from50 percent to 90 percent, preferably 60 to 80 weight percent and morepreferably 65 to 75 weight percent, all the percentages being in weightpercentage based on the total weight of composition solids.

The polyisocyanate component includes an aliphatic polyisocyanate havingon an average 2 to 6, preferably 2.5 to 6 and more preferably 3 to 4isocyanate functionalities. The coating composition includes in therange of from 25 percent to 55 percent, preferably in the range of from30 percent to 50 percent, and most preferably in the range of 35 percentto 45 percent of the polyisocyanate component, the percentages being inweight percentages based on the total weight of composition solids.

Examples of suitable aliphatic polyisocyanates include aliphatic orcycloaliphatic di-, tri- or tetra-isocyanates, including polyisocyanateshaving isocyanurate structural units such as, the isocyanurate ofhexamethylene diisocyanate and isocyanurate of isophorone diisocyanate;the adduct of 2 molecules of a diisocyanate, such as hexamethylenediisocyanate; uretidiones of examethylene diisocyanate; uretidiones ofisophorone diisocyanate or sophorone diisocyanate; isocyanurate ofmeta-tetramethylxylylene diisocyanate; and a diol such as, ethyleneglycol, the adduct of 3 molecules of hexamethylene diisocyanate and 1molecule of water (available under the trademark Desmodur® N of BayerCorporation, Pittsburgh, Pa.). Low molecular weight (400 to 1500 GPCnumber average molecular weight) adduct of the diisocyanates withmonomeric polyols, such as trimethylol propane are also suitablepolyisocyanates.

Aromatic polyisocyanates are not suitable for use in the presentinvention as the clear coatings resulting therefrom are too lightsensitive and tend to yellow with age and crack upon long term exposureto sunlight. As a result such clear coatings are not durable.

If desired, the isocyanate functionalities of the polyisocyanate may becapped with a monomeric alcohol to prevent premature crosslinking in aone-pack composition. Some suitable monomeric alcohols include methanol,ethanol, propanol, butanol, isopropanol, isobutanol, hexanol,2-ethylhexanol and cyclohexanol.

The coating composition includes in the range of from 10 percent to 40percent, preferably in the range of from 20 percent to 40 percent, andmost preferably in the range of from of 25 percent to 35 percent of themelamine component, the percentages being in weight percentages based onthe total weight of composition solids. The melamine component of thecoating composition includes suitable monomeric or polymeric melaminesor a combination thereof. Alkoxy monomeric melamines are preferred.

In the context of the present invention, the term “alkoxy monomericmelamine” means a low molecular weight melamine which contains, on anaverage three or more methylol groups etherized with a C₁ to ₅monohydric alcohol such as methanol, n-butanol, or isobutanol pertriazine nucleus, and has an average degree of condensation up to about2 and preferably in the range of about 1.1 to about 1.8, and has aproportion of mononuclear species not less than about 50 percent byweight. The polymeric melamines have an average degree of condensationof more than 1.9.

Some of such suitable monomeric melamines include highly alkylatedmelamines, such as methylated, butylated, isobutylated melamines andmixtures thereof. More particularly hexamethylol melamine, trimethylolmelamine, partially methylated hexamethylol melamine, andpentamethoxymethyl melamine are preferred. Hexamethylol melamine andpartially methylated hexamethylol melamine are more preferred andhexamethylol melamine is most preferred.

Many of these suitable monomeric melamines are supplied commercially.For example, Cytec Industries Inc., West Patterson, N.J. supplies Cymel®301 (degree of polymerization of 1.5, 95% methyl and 5% methylol),Cymel® 350 (degree of polymerization of 1.6, 84% methyl and 16%methylol), 303, 325, 327 and 370, which are all monomeric melamines.Suitable polymeric melamines include high amino (partially alkylated,—N, —H) melamine known as Resimene™ m BMP5503 (molecular weight 690,polydispersity of 1.98, 56% buytl, 44% amino), which is supplied bySolutia Inc., St. Louis, Mo., or Cymel® 1158 provided by CytecIndustries Inc., West Patterson, N.J.

Cytec Industries Inc. also supplies Cymel® 1130 @ 80 percent solids(degree of polymerization of 2.5), Cymel® 1133 (48% methyl, 4% methyloland 48% butyl), both of which are polymeric melamines.

The coating composition preferably includes one or more catalysts toenhance crosslinking of the components on curing. Generally, the coatingcomposition includes in the range of from 0.1 percent to 5 percent,preferably in the range of from 0.1 to 2 percent, more preferably in therange of from 0.5 percent to 2 percent and most preferably in the rangeof from 0.5 percent to 1.2 percent of the catalyst, the percentagesbeing in weight percentages based on the total weight of the polyesterpolyol, polyisocyanate and melamine components.

Some of the suitable catalysts include the conventional acid catalysts,such as aromatic sulfonic acids, for example dodecylbenzene sulfonicacid, para-toluenesulfonic acid and dinonylnaphthalene sulfonic acid,all of which are either unblocked or blocked with an amine, such asdimethyl oxazolidine and 2-amino-2-methyl-1-propanol,n,n-dimethylethanolamine or a combination thereof. Other acid catalyststhat can be used are strong acids, such as phosphoric acids, moreparticularly phenyl acid phosphate, which may be unblocked or blockedwith an amine.

In addition to the foregoing, the coating composition preferablyincludes a small amount of one or more organo tin catalysts, such asdibutyl tin dilaurate, dibutyl tin diacetate, stannous octate, anddibutyl tin oxide. Dibutyl tin dilaurate is preferred. The amount oforgano tin catalyst added generally ranges from 0.001 percent to 0.5percent, preferably from 0.05 percent to 0.2 percent and more preferablyfrom 0.1 percent to 0.15 percent, the percentages being in weightpercentages based on the total weight of the polyester polyol,polyisocyanate and melamine components. These catalysts are preferablyadded to the melamine component.

The coating composition includes in the range of from 5 percent to 65percent, preferably in the range of from 10 percent to 50 percent, andmost preferably in the range of from of 20 percent to 40 percent of thepolyester polyol component, the percentages being in weight percentagesbased on the total weight of composition solids.

The polyester polyol suitable for use in the polyester polyol componenthas a GPC weight average molecular weight not exceeding 3000, preferablyin the range of from 400 to 3000, more preferably in the range of 600 to2000, most preferably in the range of 800 to 1500. The polyester polyolhas hydroxyl functionality in the range from 2.2 to 6, preferably 2.5 to5 and more preferably in the range of from 2.8 to 4.0.

The polyester polyol suitable for use in the present invention may beconventionally polymerized from suitable polyacids, includingcycloaliphatic polycarboxylic acids or anhydrides, and an excess amountof suitable polyol, including polyhydric alcohol, to provide thepolyester with hydroxyl functionalities.

Examples of suitable cycloaliphatic polycarboxylic acids aretetrahydrophthalic acid (or anhydride), hexahydrophthalic acid (oranhydride), 1,2-cyclohexanedicarboxylic acid (or anhydride),1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid,4-methylhexahydrophthalic acid (or anhydride),endomethylenetetrahydrophthalic acid, tricyclodecanedicarboxylic acid,endoethylenehexahydrophthalic acid, camphoric acid,cyclohexanetetracarboxylic acid, cyclobutanetetracarboxylic acid andcombinations thereof. The cycloaliphatic polycarboxylic acids can beused not only in their cis but also in their trans form and as a mixtureof both these forms. The preferred cycloaliphatic polycarboxylic acidsare tetrahydrophthalic acid (or anhydride), hexahydrophthalic acid (oranhydride), 1,2-cyclohexanedicarboxylic acid (or anhydride),1,4-cyclohexanedicarboxylic acid and 4-methylhexahydrophthalic acid (oranhydride).

Examples of suitable polycarboxylic acids, which, if desired, can beused together with the cycloaliphatic polycarboxylic acids (oranhydrides), are aromatic and aliphatic polycarboxylic acids, such as,for example, phthalic acid; isophthalic acid; terephthalic acid,halogenophthalic acids, such as, tetrachloro- or tetrabromophthalicacid; adipic acid; glutaric acid; azelaic acid; sebacic acid; fumaricacid; maleic acid; trimellitic acid and pyromellitic acid. The preferredpolycarboxylic acids are phthalic acid and maleic acid. Generally, 0 to25 weight percent, preferably 10 to 20 weight percent of polycarboxylicacid may be added to cycloaliphatic polycarboxylic acid (or anhydride),all weight percentages being based on the total weight of polycarboxylicacid and cycloaliphatic polycarboxylic acid (or anhydride).

Suitable polyhydric alcohols include ethylene glycol, propanediols,butanediols, hexanediols, neopentylglycol, diethylene glycol,cyclohexanediol, cyclohexanedimethanol, trimethylpentanediol,ethylbutyipropanediol, ditrimethylolpropane, trimethylolethane,trimethylolpropane, glycerol, pentaerythritol, dipentaerythritol,polyalkylene glycol, such as polyethylene glycol and polypropyleneglycol. The preferred polyhydric alcohols are ditrimethylolpropane,trimethylolethane, trimethylolpropane and pentaerythritol.

A more preferred method of preparing the polyester polyol of the presentinvention is by first reacting a multifunctional alcohol, such as,pentaerythritol, hexandiol, or trimethyol propane with alicyclicmonomeric anhydrides, for example, hexahydrophthalic anhydride ormethylhexahydrophthalic anhydride to produce an oligomeric acid.Mixtures of the foregoing anhydrides may also be used. Non-alicyclicanhydrides, for example, succinic anhydride or phthalic anhydride couldalso be added to the alicyclic monomeric anhydrides. Oligomeric acidshaving at least one hydroxyl functionality are also suitable, which areprepared by reacting the multifunctional alcohol with less than astochiometric amount of the monomeric anhydride.

The oligomeric acid is then reacted with a monofunctional epoxy toproduce the polyester polyol. The oligomerization is generally carriedout at a reaction temperature in the range of from 60° C. to 200° C.preferably in the range of from 80° C. to 170° C., and more preferablyin the range of from 90° C. to 150° C. Typical reaction time is in therange of from 1 hours to 24 hours, preferably 1 hour to 4 hours.

The foregoing two-step process ensures that the hydroxyl functionalitiesare uniformly distributed on each oligomeric chain of the polyesterpolyol.

The monofunctional epoxy suitable for use in the present inventionincludes alkylene oxide of 2 to 12 carbon atoms such as ethylene,propylene and butylene oxides. Other epoxies, such as, Glydexx®N-10glycidyl ester, supplied by Exxon Chemicals, Houston, Tex. may be usedalone or in combination with other alkylene oxide monomers.

The coating composition of the present invention, which is formulatedinto high solids coating systems further contains at least one organicsolvent typically selected from the group consisting of aromatichydrocarbons, such as petroleum naphtha or xylenes: ketones, such as,methyl amyl ketone, methyl isobutyl ketone. methyl ethyl ketone oracetone; esters, such as, butyl acetate or hexyl acetate, and glycolether esters, such as propylene glycol monomethyl ether acetate. Theamount of organic solvent added depends upon the desired solids level aswell as the desired amount of VOC of the composition. If desired, theorganic solvent may be added to both components of the binder.

The coating composition of the present invention may also containconventional additives, such as stabilizers, and rheology controlagents, flow agents, and toughening agents. Such additional additiveswill, of course, depend on the intended use of the coating composition.Any additives that would adversely effect the clarity of the curedcoating will not be included as the composition is used as a clearcoating. The foregoing additives may be added to either component orboth, depending upon the intended use of the coating composition.

The clear coating composition of the present invention may be suppliedin the form of a two-pack coating composition in which the first-packincludes the polyisocyanate component and the second-pack includes themelamine component. Generally the first and the second pack are storedin separate containers and mixed before use. The containers arepreferably sealed air tight to prevent degradation during storage. Themixing may be done, for example, in a mixing nozzle or in a container.

Alternatively, when the isocyanates functionalities of thepolyisocyanate are blocked, both the components of the coatingcomposition can be stored in the same container in the form of aone-pack coating composition.

The coating composition of the present invention optionally contains inthe range of from 0.1 percent to 40 percent, preferably in the range offrom 5 percent to 35 percent, and more preferably in the range of from10 percent to 30 percent of a flow modifying resin, such as anon-aqueous dispersion (AND), all percentages being based on the totalweight of composition solids. The weight average molecular weight of theflow modifying resin generally varies in the range of from 20,000 to100,000, preferably in the range of from 25,000 to 80,000 and morepreferably in the range from 30,000 to 50,000.

The non-aqueous dispersion-type resin is prepared bydispersion-polymerizing at least one vinyl monomer in the presence of apolymer dispersion stabilizer and an organic solvent. The polymerdispersion stabilizer may be any of the known stabilizers used commonlyin the field of non-aqueous dispersions, and may include the followingsubstances (1) through (9) as examples:

(1) A polyester macromer having about 1.0 polymerizable double bondwithin the molecule as obtainable upon addition of glycidyl acrylate orglycidyl methacrylate to an auto-condensation polyester of ahydroxy-containing fatty acid such as 12-hydroxystearic acid.

(2) A comb-type polymer prepared by copolymerizing the polyestermacromer mentioned under (1) with methyl methacrylate and/or other(meth)acrylic ester or a vinyl monomer.

(3) A polymer obtainable by the steps of copolymerizing the polymerdescribed under (2) with a small amount of glycidyl (meth)acrylate and,then, adding (meth)acrylic acid to the glycidyl groups thereof so as tointroduce double bonds.

(4) A hydroxy-containing acrylic copolymer prepared by copolymerizing atleast 20 percent by weight of (meth)acrylic ester of a monohydricalcohol containing 4 or more carbon atoms.

(5) An acrylic copolymer obtainable by producing at least 0.3 doublebond per molecule based on its number average molecular weight, into thecopolymer mentioned under (4). A method for introducing double bondsmay, for example, comprise copolymerizing the acrylic polymer with asmall amount of glycidyl (meth)acrylate and then adding (meth)acrylicacid to the glycidyl group.

(6) An alkylmelamine resin with a high tolerance to mineral spirit.

(7) An alkyd resin with an oil length not less than 15 percent and/or aresin obtainable by introducing polymerizable double bonds into thealkyd resin. A method of introducing double bonds may, for example,comprise addition reaction of glycidyl (meth)acrylate to the carboxylgroups in the alkyd resin.

(8) An oil-free polyester resin with a high tolerance to mineral spirit,an alkyd resin with an oil length less than 15 percent, and/or a resinobtainable by introducing double bonds into said alkyd resin.

(9) A cellulose acetate butyrate into which polymerizable double bondshave been introduced. An exemplary method of introducing double bondscomprises addition reaction of isocyanatoethyl methacrylate to celluloseacetate butyrate.

These dispersion stabilizers can be used alone or in combination.

Among the aforementioned dispersion stabilizers, preferred for thepurposes of the invention are those which can be dissolved incomparatively low polar solvents, such as aliphatic hydrocarbons toassure the film performance requirements to some extent. As dispersionstabilizers which can meet such conditions, the acrylic copolymersmentioned under (4) and (5) are desirable in that they not only lendthemselves well to adjustment of molecular weight, glass transitiontemperature, polarity (polymer SP value), hydroxyl value, acid value andother parameters but are excellent in weatherability. More desirable areacrylic copolymers containing an average of about 0.2 to about 1.2polymerizable double bonds, per molecule, which are graft copolymerizedwith dispersed particles.

The non-aqueous dispersion-type resin used in accordance with thisinvention can be easily prepared by dispersion-polymerizing at least onevinyl monomer in the presence of the aforedescribed polymer dispersionstabilizer and an organic solvent, which mainly contains an aliphatichydrocarbon. The dispersion stabilizer and the vinyl monomer are solublein the organic solvent. However, the polymer particles formed by thevinyl monomer are not soluble in the solvent.

The monomer component forming the acrylic copolymer suitable as thepolymer dispersion stabilizer and the vinyl monomer forming thedispersed particles may be virtually any radical-polymerizableunsaturated monomer. A variety of monomers can be utilized for thepurpose. Typical examples of such monomers include the following.

(a) Esters of acrylic acid or methacrylic acid, such as for example,C₁₋₁₈ alkyl esters of acrylic or methacrylic acid, such as methylacrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butlacrylate, hexyl acrylate, octyl acrylate, lauryl acrylate, stearylacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate,isopropyl methacrylate, butyl methacrylate, hexyl methacrylate, octylmethacrylate, lauryl methacrylate, and stearyl methacrylate; glycidylacrylate and glycidyl methacrylate; C₂₋₈ alkenyl esters of acrylic ormethacrylic acid, such as allyl acrylate, and allyl methacrylate; C₂₋₈hydroxyalkyl esters of acrylic or methacrylic acid, such as hydroxyethylacrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, andhydroxypropyl methacrylate; and C₃₋₁₈ alkenyloxyalkyl esters or acrylicor methacrylic acid, such as allyloxyethyl acrylate, and allyloxyethylmethacrylate.

(b) Vinyl aromatic compounds, such as for example styrene,alpha-methylstyrene, vinyltoluene, p-chlorostyrene, and vinylpyridine.

(c) α, β-Ethylenically unsaturated acids, such as, for example, acrylicacid, methacrylic acid, itaconic acid and crotonic acid

(d) Amides of acrylic or methacrylic acid, such as, for example,acrylamide, methacrylamide, n-butoxymethylacrylamide,N-methylolacrylamide, n-butoxymethylmethacrylamide, andN-methylolmethacrylamide.

(e) Others: for example, acrylonitrile, methacrylonitrile, methylisopropenyl ketone, vinyl acetate, VeoVa monomer (product of ShellChemicals, Co., Ltd.; mixed vinyl esters of a synthetic saturatedmonocarboxylic acid of highly branched structure containing ten carbonatoms), vinyl propionate, vinyl pivalate, isocyanatoethyl methacrylate,perfluorocyclohexyl (meth)acrylate, p-styrenesulfonamide,N-methyl-p-styrenesulfonamide, anf γ-methacryloyloxypropyl trimethoxysilane.

Among the monomers mentioned above, the following materials can be usedwith particular advantage for the preparation of the acrylic copolymerused as a dispersion stabilizer:

Mixed monomers based on comparatively long-chain, low-polar monomers,such as n-butyl methacrylate, 2-ethylhexyl methacrylate, dodecylmethacrylate, lauryl methacrylate, and stearyl methacrylate,supplemented as necessary with styrene, methyl (meth)acrylate, ethyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate, propyl (meth)acrylate,and (meth)acrylic acid. The dispersion stabilizer may be one prepared byadding glycidyl (meth)acrylate or isocyanatoethyl methacrylate to acopolymer of the monomers for introduction of polymerizable doublebonds.

The acrylic copolymer used as the dispersion stabilizer can be easilyprepared using a radical polymerization initiator in accordance with theknown solution polymerization process.

The number average molecular weight of the dispersion stabilizer ispreferably in the range of about 1,000 to about 50,000 and, for stillbetter results, about 3,000 to about 20,000.

Among the monomers mentioned above, particularly preferred vinylmonomers for the formation of the dispersed polymer particlespredominantly contain comparatively high-polarity monomers, such asmethyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, andacrylonitrile, supplemented as necessary with (meth)-acrylic acid, and2-hydroxyethyl (meth)acrylate. It is also possible to provide gelparticles as cross-linked in molecules by copolymerizing a small amountof polyfunctional monomers, such as divinylbenzene, and ethylene glycoldimethacrylate, by copolymerizing a plurality of monomers havingmutually reactive functional groups, such as glycidyl methacrylate andmethacrylic acid, or by copolymerizing an auto-reactive monomer, such asN-alkoxymethylated acrylamides, and γ-methacryloyloxypropyl trimethoxysilanes.

In conducting the dispersion polymerization, the ratio of the dispersionstabilizer to the vinyl monomer forming dispersed particles is selectedfrom the range of about 5/95 to about 80/20 by weight, preferably about10/90 to about 60/40 by weight, and the dispersion polymerization can beconducted in the presence of a radical polymerization initiator by aknown procedure.

While the particle size of the resulting non-aqueous dispersion typeacrylic resin is generally in the range of about 0.05 μm to about 2 μm,the range of about 0.1 μm to about 0.7 μm is preferable from thestability of shelf life and the gloss, smoothness and weatherability ofthe film.

To improve weatherability of the coating, 0.1-5 weight percent,preferably 1 to 2.5 weight percent and more preferably 1.5 to 2 weightpercent, based on the weight of the total weight of the polyester,polyisocyanate and melamine components, of an ultraviolet lightstabilizer or a combination of ultraviolet light stabilizers can beadded. These stabilizers include ultraviolet light absorbers andhindered amine light stabilizers.

Typical ultraviolet light stabilizers that are useful are as follows:

Benzophenones, such as hydroxydodecylbenzophenone,2,4-dihydroxybenzophenone, hydroxybenzophenones containing sulfonic acidgroups, 2,4-dihydroxy-3′,5′-di-t-butylbenzophenone,2,2′,4′-trihydroxybenzophenone esters of dicarboxylic acids,2-hydroxy-4-acryloxyethoxybenzophenone, aliphatic mono-esters of2,2′,4′trihydroxy-4′-alkoxy-benzophenone,2-hydroxy-4-methoxy-2′-carboxybenzophenone.

Triazoles, such as 2-phenyl-4-(2′,4′-dihydroxybenzoyl) triazoles,substituted benzotriazoles, such as hydroxyphenyltriazoles including2-(2′hydroxy-5′-methylphenyl) benzotriazole, 2-(2′hydroxyphenyl)benotriazole, 2-(2′hydroxy-5′-octylphenyl) naphthotriazole.

Triazines, such as 3,5-dialkyl-4-hydroxyphenyl derivatives of triazine,sulfur-containing derivatives of dialkyl-4-hydroxyphenyltriazines,hydroxyphenyl-1,3,5-triazines and triazines containing sulfonic acidgroups, such as aryl-1,3,5-triazines, orthohydroxyaryl-s-triazine.

Benzoates, such as dibenzoate of diphenylopropane, t-butyl benzoate ofdiphenylopropane, nonyl phenyl benzoate, octyl phenyl benzoate,resorcinol dibenzoate.

Other ultraviolet light stabilizers that can be used include lower alkylthiomethylene-containing phenols, substituted benzenes, such as1,3-bis(2′-hydroxybenzoyl) benzene, metal derivatives of 3,5′-di-t-butyl4-hydroxyphenylpropionic acid, asymmetrical oxalic acid diarylamides,alkylhdroxyphenylthioalkanoic acid esters, dialkylhydroxyphenylalkanoicacid esters of di- and tri-pentaerythritol, phenyl- andnaphthlene-substituted oxalic acid diamides,methyl-.beta.-(3,5-di-t-butyl-4-hydroxyphenyl) propionate, α, α′-bis(2hydroxy-phenyl) diisopropylbenzene, 3,5′-dibromo-2′-hydroxyacetophenone,ester derivatives of 4,4-bis(4′-hydroxy-phenyl) pentaonic acid whereinthere is at least one unsubstituted position ortho to the aromatichydroxyl groups, organophosphorus sulfides such asbis(diphenylphosphinothioyl) monosulfide andbis(diphenyl-phosphinothioyl) dislufide,4-benzoyl-6-(dialkylhydroxybenzyl) resorcinol,bis(3-hydroxy-4-benzoylphenoxy) diphenylsilane,bis(3-hydroxy-4-benzoylphenoxy) dialkylsilane, 1,8-naphthalimides,α-cyano β, β-diphenylacrylic acid derivatives, bis(2-benzoxazoly)alkanes, methylene malonitriles containing aryl and heteroacyclicsubstitutes, alkylene bis (dithio) carbarnate,4-benzoyl-3-hydroxy-phenoxyethyl acrylate,4-benzoyl-3-hydroxyphenoxyethyl methacrylate, aryl or alkyl-substitutedacrylonitriles, 3-methyl-5-isopropylphenyl-6-hydroxycourmarone,8-acetyl-3-dodecyl-7,7,9,9-tetramethyl- 1,3,8-triazasprio (4,5)decanol-2,4-dione.

Particularly useful ultraviolet light stabilizers that can be used arehindered amines of piperidyl derivatives, such as those disclosed inMurayama et al., U.S. Pat. No. 4,061,616, issued Dec. 6, 1977, column 2,line 65, through column 4, line 2, and nickel compounds such as[1-phenyl-3-methyl-4-decanoylpyrazolate(5)]-Ni,bis[phenyldithiocarbamato]-Ni(II), and others listed in the abovepatent, column 8, line 44 through line 55.

In use, the first-pack of the two-pack coating composition containingthe polyisocyanate and the second-pack containing the melamine andpolyester polyol component are mixed just prior to use or about 5 to 30minutes before use to form a pot mix, which has limited pot life ofabout 10 minutes to about 6 hours. Thereafter, it becomes too viscous topermit application through conventional application systems, such asspraying. A layer of the pot mix is typically applied to a substrate byconventional techniques, such as spraying, electrostatic spraying,roller coating, dipping or brushing. Generally, a clear coat layerhaving a thickness in the range of from 25 micrometers to 75 micrometersis applied over a metal substrate, such as automotive body, which isoften pre-coated with other coating layers, such as an electrocoat,primer and a basecoat. The two pack coating composition may be bakedupon application for about 60 to 10 minutes at about 80° C. to 160° C.

When the one-pack coating composition containing the blockedpolyisocyanate is used, a layer thereof applied over a substrate usingaforedescribed application techniques, is cured at a baking temperaturein the range of from 80° C. to 200° C., preferably in the range of 80°C. to 160° C., for about 60 to 10 minutes. It is understood that actualbaking temperature would vary depending upon the catalyst and the amountthereof, thickness of the layer being cured and the blocked isocyanatefunctionalities and the melamine utilized in the coating composition.The use of the foregoing baking step is particularly useful under OEM(Original Equipment Manufacture) conditions.

If desired, the composition can be pigmented to form a colored finish orprimer. About 0.1-200% by weight, based on the weight of the binder, ofconventional pigments can be added using conventional techniques inwhich a mill base containing pigment, dispersant and solvent is firstformed. The mill base is then mixed with the composition to form acolored composition. This composition can be applied and cured as shownabove.

The clear coating composition of the present invention is suitable forproviding clear coatings on variety of substrates, such as metal, woodand concrete substrates. The present composition is especially suitablefor providing clear coatings in automotive OEM or refinish applicationstypically used in coating autobodies. These compositions are alsosuitable as clear coatings in industrial and maintenance coatingapplications.

The invention is illustrated in the following Examples:

EXAMPLES Polyester Polyol A

This was the reaction product of trimethylol propane, methylhexahydrophthalic anhydride and ethylene oxide. The ingredients areshown in Table 1 below. The PGMEA, TMP and TEA were charged to a vesselrated for high pressure and heated to 140° C. The MHHPA was added to thereactor over one hour and then the batch was held at 140° C. for sixhours. Thereafter the batch was cooled to 25° C. The vessel was sealedand the EO was added. The batch was heated to 110° C. and held for sixhours. The excess EO was purged from the reactor with nitrogen. Thematerial had a Gardner Holdt viscosity of F and solids at 64.3%. Theacid number was 10. The batch was then stripped to 85% solids.

TABLE 1 TMP Trimethylol propane 134 grams PGMEA Propylene glycolmonomethyl ether acetate 565 grams MHHPA¹ Methyl hexahydrophthalicanhydride 491 grams TEA Triethylamine 0.23 grams EO Ethylene Oxide 198grams ¹Milldride ® anhydride supplied by Milliken Chemical

Polyester Polyol B

This was the reaction product of TMMP, MHHPA and glycidyl ester Theingredient amounts are shown in Table 2 below.

The TMP and PGMEA (propylene glycol monomethyl ether acetate) werecharged to a four-neck flask fitted with a condenser, stirrer, droppingfunnel and thermometer. The batch was heated to reflux (approx. 145°C.). The MHHPA was added dropwise, evenly, over 60 minutes. The reactionwas then continued at reflux for four hours. The reaction was thenreduced to 120° C., the DMEA was added and then the Cardura®E glycidylester was added evenly over 60 minutes. The reaction temperature wasraised to 140° C. and held until an acid number of less than 4 wasachieved. The resultant product had a viscosity of Z on the GardnerHoldt scale and percent solids of 80%.

TABLE 2 TMP Trimethylol propane 268 grams PGMEA Propylene glycolmonomethyl 690 grams ether acetate MHHPA¹ Methyl hexahydrophthalicanhydride 974 grams DMEA Dimethylethanol amine 0.4 grams Cardura ®EGlycidyl ester of C9 aliphatic acid 1520 grams ¹Milldride ® anhydridesupplied by Milliken Chemical

The following examples along with comparative examples describe theclearcoat composition of the present invention as well as the propertiesof clearcoats obtained therefrom when sprayed over basecoats and cured.

The components of part A in each Example were well mixed, combined withPart B material (polyisocyanate) and then sprayed over basecoat withinthirty minutes of mixing. The basecoat was a commercial waterborne blackbasecoat sprayed to give 15.2 micrometer (0.6 mils) of film thickness.The basecoat was prebaked for 10 minutes at 82° C. (180° F.). Theclearcoats were sprayed to give 51±5.1 micrometers (2.0±0.2 mils) offilm thickness and then baked for thirty minutes at 141° C. (285° F.).

The examples show variation of the three components (polyester polyol,melamine resin and polyisocyanate) in amounts and type.

Comparative Example 1 and Examples 2 to 4

TABLE 3 Compar- Examples ative 1 2 3 4 Ratio (Polyol/Mel/lso) 15/20/6525/20/55 35/20/45 45/20/35 Part A Polyester Polyol A¹ 17.6 29.4 41.252.9 Cymel ® 1158 25.0 25.0 250 25.0 melamine³ Tinuvin ® 928 UV 2.0 2.02.0 2.0 absorber⁴ Tinuvin ® 152 light 1.0 1.0 1.0 1.0 stabilizer⁴ 10%Byk ® 301 1.0 1.0 1.0 1.0 flowcontrol additive⁵ 10% catalyst⁷ 0.5 0.50.5 0.5 Phenyl Acid Phosphate 0.7 0.7 0.7 0.7 (catalyst) EthoxyethylPropionate 8.0 12.0 12.0 12.0 solvent Solvesso 100 solvent 3.0 6.0 PartB 83% polyisocyanate⁸ 78.3 66.3 54.2 45.2 Viscosity (Part A) in 58 60 5551 seconds⁹ Tukon Hardness 5.6 12.2 13.5 15.7 (ASTM D1474) CrockmeterMar¹⁰ 78 85 78 82 Etch Resistance¹¹ 0 −4 −6 -3 Equal Slightly SlightlyEqual better better

Examples 5 and 6

TABLE 4 Example 5 6 Ratio (Polyol/Mel/lso) 40/30/30 20/30/50 Part APolyester Polyol B2 51.0 25.5 Cymel ® 1158 melamine³ 37.5 37.5 Tinuvin ®928 UV absorber⁴ 2.0 2.0 Tinuvin ® 152 light stabilizer⁴ 1.0 1.0Polybutyl Acrylate⁶ 0.5 0.5 10% catalyst⁷ 0.5 0.5 Phenyl Acid Phosphate0.7 0.7 (catalyst) Ethoxyethyl Propionate 10.0 10.0 (solvent) Solvesso100 solvent 6.0 5.0 Part B 83% polyisocyanate⁸ 36.1 42.2 Viscosity (PartA) in seconds⁹ 60 60 Tukon Hardness 12.7 10.4 (ASTM D1474) CrockmeterMar¹⁰ 86 83 Etch Resistance¹¹ −10 −10 better Better Notes for Tables 4and 4 above and Table 5 below ¹Polyester polyol A described earlier²Polyester polyol B described earlier ³A product of Cytec Industries,Inc., Stamford, Connecticut ⁴A product of Ciba Specialty ChemicalsCorp., Tarrytown, NY. ⁵A product of BYK-Chemie USA, Wallingford,Connecticut ⁶A polymer of butyl acrylate at 60% solids in xylene, Mw =8400 ⁷10% solution of dibutyl tin dilaurate in ethoxyethylpropionate(EEP) ⁸An 83% solution of Tolonate ®HDT-LV, a product of Rhodia,Cranbury New Jersey ⁹#4 Ford cup ¹⁰Crockmeter - Dry Mar Resistance-Panels, which have cured clearcoat over black basecoats were coated witha thin layer of Bon Ami abrasive supplied by Faultless Starch/Bon AmiCorporation, Kansas City, Missouri. The clear coats had a dry coatingthickness of 50 microns. The panels were then tested for mar damage for10 double rubs #against a green felt wrapped fingertip of A.A.T.C.C.Crockmeter (Model CM-1, Atlas Electric Devices Corporation, Chicago,Illinois). The dry mar resistance was recorded as percentage of glossretention by measuring the 20° gloss of the marred areas versusnon-marred areas of the coated panels. ¹¹Damage caused by spots of a pH1 solution applied to a panel resting on a gradient oven. The spots areapplied at 5° C. intervals from 40° C. to 85° C. for 30 minutes. Thedegree of damage is compared to a commercial two component urethaneautomotive clearcoat. Negative numbers mean less damage vs. control.Higher the negative number #better the etch resistance against thestandard. Deviation of four units from the standard is consideredsignificant.

The following are considered to be acceptable coating properties: Acoating composition viscosity of 80 seconds and lower, Tukon hardness ofthe resultant coating of 7.5 and higher, and a Crockmeter mar reading ofthe resultant coating of 75 and higher.

From the foregoing Examples it can be seen that when more than 50 weightpercent of polyisocyanate is used in a coating composition (ComparativeExample 1) the coating hardness suffers. As the amount of polyesterpolyol is increased, the coating composition viscosity drops withoutsubstantially affecting other properties (Examples 2, 3 and 4). As theamount of polyisocyanate is increased, etch resistance is improved(Example 5 and 6).

Comparative Examples

Comparative Examples 7 and 8 illustrate how the coating properties areaffected when one of the essential (polyester polyol, melamine, andpolyisocyanate) components of the present invention is absent. InComparative Example 7, there is no melamine resin. The coating resultingtherefrom had only marginal etch resistance and the mar resistance wasvery poor. In Comparative Example 8, there was no polyisocvanate. Inthis case, the mar resistance was good, but the etch resistance waspoor. Thus, it is seen that the applicants have unexpectedly discoveredthat it is the combination of these components present in the highsolids low VOC coating composition that provides good etch and marresistance, while still having desired application viscosities.

TABLE 5 Comparative Examples 7 8 Ratio (Polyol/Mel/lso) 58/0/42 65/35/0Part A Polyester Polyol A¹ 68.2 76.5 Cymel ® 303 melamine³ 35.0Tinuvin ® 928 UV 2.0 2.0 absorber⁴ Tinuvin ® 152 light 1.0 1.0stabilizer⁴ Polybutyl Acrylate⁶ 0.5 0.5 Dodecylbenzene sulfonic acid 1.3Phenyl Acid Phosphate 0.7 (catalyst) Ethoxyethyl Propionate 12.0 12.0(solvent) Solvesso 100 solvent 6.0 15.0 90.4 141.3 Part B 83%polyisocyanate⁸ 50.6 Viscosity (Part A) in seconds⁹ 52 60 Tukon Hardness12.3 14.5 (ASTM D1474) Crockmeter Mar¹⁰ 24 85 Etch Resistance¹¹ 0 +10equal Poor

What is claimed is:
 1. A clear coating composition comprising apolyester polyol, a polyisocyanate component and a melamine componentwherein the total amount of said polyisocyanate and melamine componentsrange from 50 percent to 90 percent, said percentages being in weightpercentage based on the total weight of composition solids providedneither said polyisocyanate component nor said melamine component ismore than about half of said total weight of composition solids andwherein said polyisocyanate component comprises an aliphaticpolyisocyanate having on an average 2 to 6 isocyanate functionalities,wherein said isocyanate functionalities are unblocked or blocked byreacting with a monomeric alcohol.
 2. The composition of claim 1 whereinsaid monomeric alcohol is an aliphatic alcohol.
 3. The composition ofclaim 1 wherein said polyester polyol component comprises at least onehydroxyl polyester having in the range of 2.5 to 6 hydroxyfunctionalities and a weight average molecular weight of less than 3000.4. The composition of claim 1 wherein said composition further comprisesone or more organo tin or acid catalysts.
 5. The composition of claim 4wherein said organo tin catalyst is selected from the group consistingof dibutyl tin diacetate, dibutyl tin dilaurate, stannous octate, and acombination thereof.
 6. The composition of claim 4 wherein the acidcatalyst is selected from the group consisting of dodecylbenzenesulfonic acid, dodecylbenzene sulfonic acid blocked with an amine,para-toluenesulfonic acid, para-toluenesulfonic acid blocked with saidamine, phenyl acid phosphate, phenyl acid phosphate blocked with saidamine, dinonylnaphthalene sulfonic acid, dinonylnaphthalene sulfonicacid blocked with said amine and a combination thereof.
 7. Thecomposition of claim 6 wherein said amine is selected from the groupconsisting of dimethyl oxazolidine, 2-amino-2-methyl-1-propanol,n,n-dimethylethanolamine and a combination thereof.
 8. The compositionof claim 4, 5, or 6 wherein said composition comprises in the range offrom 0.001 percent to 5.0 percent of said catalyst, all percentagesbeing weight percentages based on the total weight of polyester polyol,polyisocyanate and melamine components.
 9. The composition of claim 1wherein said polyisocyanate component is selected from the groupconsisting of one or more trimers of hexamethylene diisocyanate,isophorone diisocyanate, meta-tetramethylxylylene diisocyanate, and acombination thereof.
 10. The composition of claim 1 or 5 comprises inthe range of from 25 percent to 55 percent said polyisocyanate componentwherein all percentages are in weight based on the total weight ofcomposition solids.
 11. The composition of claim 1, 2 or 9 wherein saidpolyisocyanate component has an average of 2.5 to 6 isocyanatefunctionalities.
 12. The composition of claim 1 wherein said melaminecomponent is selected from the group consisting of a monomeric melamine,a polymeric melamine, and a combination thereof.
 13. The composition ofclaim 1 or 12 comprises in the range of from 10 percent to 40 percent ofsaid melamine component wherein all percentages are in weight based onthe total weight of composition solids.
 14. The composition of claim 1further comprises a flow modifying resin having a weight averagemolecular weight in the range of 20,000 to 100,000.
 15. The compositionof claim 1 comprises in the range of from 5 percent to 65 percent ofsaid polyester polyol component, all percentages being in weightpercentages based on the total weight of composition solids.
 16. Thecomposition of claim 1 in the form of a two-pack composition wherein afirst-pack of said two-pack composition comprises said melamine and saidpolyester polyol component and a second-pack of said two-packcomposition comprises said polyisocyanate component.
 17. The compositionof claim 1 wherein a volatile organic component of said compositionvaries in the range of from 0.0 to 0.472 kilogram of an organic solventper liter of the composition.
 18. The clear coating composition of claim1 wherein a clear coating on a substrate produced from said compositionhas a distinctness of image rating of at least
 80. 19. The compositionof claim 1 further comprises components selected from the groupconsisting of ultra violet light stabilizers, light absorbers and acombination thereof.
 20. A method of producing a clear coating on asubstrate comprising: applying a layer of a clear coating compositioncomprising a polyester polyol, a polyisocyanate component and a melaminecomponent wherein the total amount of said polyisocyanate and melaminecomponents range from 50 percent to 90 percent, said percentages beingin weight percentage based on the total weight of composition solidsprovided neither said polyisocyanate component nor said melaminecomponent is more than about half of said total weight of compositionsolids and wherein said polyisocyanate component comprises an aliphaticpolyisocyanate having on an average 2 to 6 isocyanate functionalities,wherein said isocyanate functionalities are unblocked or blocked byreacting with a monomeric alcohol; and curing said layer into said clearcoating.
 21. The method of claim 20 wherein said coating has adistinctness of image rating of at least
 80. 22. The method of claim 21wherein said coating has a 20° gloss of at least
 80. 23. The method ofclaim 22 wherein said isocyanate functionalities of the polyisocyanateare blocked by reacting said polyisocyanate with a monomeric alcohol.24. The method of claim 23 wherein said monomeric alcohol is selectedfrom the group consisting of cyclohexanol, 2-ethyl hexanol and a mixturethereof.
 25. The method of claim 23 or 24 wherein said curing of saidlayer takes place at an elevated baking temperature in the range 80° C.to 160° C.
 26. The method of claim 22 wherein said composition comprisesin the range of from 5 percent to 65 percent of said polyester polyolcomponent, all percentages being in weight percentages based on thetotal weight of composition solids.